The present invention relates to a single or multiple-layer foil of substantially reduced gas-permeability, and a method of producing a single-layer or multiple-layer foil, a polymer blend consisting of a polyolefin and starch, a method of producing the polymer blend, thermoplastically processable starch, a method of producing thermoplastically processable starch, a foil consisting of a polymer blend, and a shaped body consisting of a polymer blend.
For the packaging of, for instance, oxygen-sensitive materials such as foodstuffs, it is important that the packing means be of low gas-permeability, i.e. have a low oxygen permeability in the example indicated.
Further requirements on such packing materials are that they be insensitive to moisture, have sufficient mechanical properties, are transparent depending on their use and are of low price.
In particular for the packaging of foodstuffs, there are known sheets of PVC and, even of substantially more general use today, foils of polyvinylidene chloride or PVDC, such as, for instance, "Saran." The gas-permeability of these materials as well as their insensitivity to moisture are excellent. However, these materials have the great disadvantage that the disposal of them is not unobjectionable as a result of their chlorine content, since hydrogen chloride is produced upon burning.
For this reason, these chlorine-containing foils are being increasingly replaced by so-called sandwich foils, such as, for instance, multi-layer foils consisting of a layer of polyamide and a layer of polyethylene or of a layer of polyethylene and a layer of polyvinyl alcohol. There are no limits on the possibilities of variation of the different sandwich foils. In order that these different polymer materials adhere well to each other, intermediate layers of so-called block copolymers are for instance proposed which serve as so-called phase mediators.
In these sandwich foils, the polyamide layer, for example, forms a good barrier to oxygen while, on the other hand, the polyethylene layer is responsible for the impermeability to water. Depending on the properties of the individual polymers and of the required properties of the foil, the layers can be arranged in various manners. Three, four, five or multiple-layer foils, for instance, are known.
The manufacture of these multi-layer foils is, however, relatively expensive since, on the one hand, measures must be taken to see to it that there is good adherence between the individual layers and furthermore the polymers selected, such as, for example, polyamide, are relatively expensive raw materials.
Although these polymers are substantially unobjectionable as compared with chlorine-containing polymers such as PVC or PVDC, their disposal is nevertheless not without problems. Plastics consisting of polyethylene, polyamide, polypropylene, etc. are still today incinerated to a substantial extent since they are scarcely, if at all, biologically degradable. Furthermore, the so-called recycling of these plastics is scarcely possible or is possible only with difficulty.
One object of the present invention is therefore to create a foil for the packaging of materials which is of low gas-permeability, such as, for instance, oxygen permeability, and which furthermore is substantially insensitive to moisture.
Another object of the present invention is to create a polymer material which is suitable, at least in part, for the production of such a foil.